1. Field of the Invention
This invention relates to toll restricting telephone apparatus and, more particularly, to an attachment apparatus and method for preventing long distance telephone calls from being placed from a local restricted telephone set.
2. Description of the Prior Art.
It has heretofore been known to provide toll restriction circuits on various telephones in a telephone system so as to prevent the use of those telephones for long distance telephone calls for obvious reasons of economy. In the prior art system of which I have knowledge, restrictive equipment was maintained at the central station which received the full information on the called number, determined whether the called number was a long distance call, and determined whether the telephone station from which the call was placed is authorized to make such long distance calls and when that determination was negative the line was disabled and the call was not completed. Currently many users install private automatic branch exchanges (PABX) which they interconnect to telephone company lines. Ideally it is desired to restrict some of the telephone stations within the PABX system from initiating off-premises long distance telephone calls without disturbing the other substations therein or without requiring the installation of expensive circuitry of the aforementioned type frequency found in central stations. Toll restricting devices for the foregoing application have been made known to me in U.S. Pat. No. 3,727,007 to Catlin, granted Apr. 10, 1973, and in U.S. Pat. No. 3,757,055 to McCann, granted Sept. 4, 1973. In each of the toll restrictors disclosed in the aforecited patents means are provided to terminate the placement of the telephone call if the number of digits dialed exceeds that necessary for a local call or if the initial digit or digits dialed represents an attempt to reach a long distance telephone operator. The present invention is directed to a similar type of toll restricting apparatus.